Compared with LCD (liquid crystal display), organic light-emitting diode (OLED) is advantageous in being self-luminous, quick response, wide viewing angle, high brightness, vivid color, being light and thin, and so on, and is deemed as the next generation display technology.
Film formation of the OLED material mainly includes evaporation process and solution process. The evaporation process is mature in small size application, and currently this technology has been used in mass production. The solution process for film formation of the OLED material includes inkjet printing, spray coating, spin coating, screen printing, and so on. Among these film formation methods, the inkjet printing technology is expected to be the main method for achieving mass production of the large size OLED due to its higher material utilization and its ability of achieving large size.
In the inkjet printing process, it is necessary to form pixel defining layers (PDL) on electrodes of a substrate in advance, to define ink droplets of the organic light-emitting material to precisely flow into a designated R/G/B sub pixel areas.
The cross section shape of the PDL structure may have two kinds, including regular trapezoid shape (as shown in FIG. 1) and inverted trapezoid shape (as shown in FIG. 2). The regular trapezoid shaped structure illustrated in FIG. 1 is widely used, with an array of first electrodes 120 on a planarization layer 110 and the PDLs 130 are arranged between the first electrodes 120. FIG. 2 shows another structure in which an array of the first electrodes 220 is arranged on a planarization layer 210, the PDLs 230 are arranged between the first electrodes 220, and each of the PDLs 230 has the inverted trapezoid structure.